UTILIZING NONUNIFORM COUPLED TRANSMISSION LINES TO COMPACT MICROSTRIP CIRCUITS SUCH AS EDGE-COUPLED BANDPASS FILTERS

In this paper, we propose a method to reduce the length of the narrowband microstrip Uniform Coupled Transmission Lines (UCTLs), which has a general application to compact microstrip circuits. In this method, we use Nonuniform Coupled Transmission Lines (NCTLs) instead of UCTLs. To synthesize the desired NCTLs, their normalized width and gap are expanded as two truncated Fourier series. Then, the optimal values of the coe-cients of the series are obtained through an optimization approach. The usefulness of the proposed method is verifled using some examples. Also, an edged- coupled bandpass fllter is compacted using the proposed method and then is fabricated and measured.